The use of explosives in public and mining works is so common that today undertaking such activities without their use would be unthinkable. Given the nature of these products, the issue of safety as much in their handling as in their transportation to the place of use are very important and constitute the priority area in the research and development in this industry.
The market has evolved from the use of cartridge-packaged products, generally cap sensitive, to much less sensitive products that should be initiated with a booster. To facilitate transport the tendency is to manufacture or sensitize “in situ”.
In reference to manufacturing “in situ”, that is, in the truck used for the pumping of the explosives to the shot hole, the first patents are from IRECO (U.S. Pat. No. 3,303,738 and U.S. Pat. No. 3,338,033). These patents disclose the manufacturing inside the truck of a watergel type explosive through the dosage and mixture of a liquid solution of salts and oxidants with a solid material containing oxidizing and thickening salts. In U.S. Pat. No. 3,610,088 (IRECO) the same method is used as in the previous patents for the formation of watergel “in situ” and incorporates the simultaneous addition of air either by mechanical trapping or through the generation of a gas through a chemical reaction. The patent EP 0 203 230 (IRECO) describes a mixer composed of mobile and fixed blades that allow for “in situ” manufacturing of an water-in-oil emulsion-type explosive agent.
The principal drawback of these first generation “in situ” manufacturing techniques lies in the fact that they used oxidant salt solutions at a high temperature that had to be transported in perfectly heat-resistant tanks with a heat contribution. The complexity both of the factory truck and of the manufacturing operation required the presence of highly qualified personnel to guarantee the success of the operation.
With the advent of emulsions, the tendency moved towards transporting matrix emulsions classified as non-explosive and their sensitizing “in situ”, by mixing with hollow microspheres or generating gas via a chemical reaction. One characteristic of the emulsions is that they cannot be handled once gasified, as this provokes the migration of the gas bubbles and, therefore, an increase in density. For this reason, the pumping and handling of the emulsion should be carried out before the gasification reaction occurs, just as described in U.S. Pat. No. 4,008,108. The principal drawback of this is the time lapse between filling the shot holes and reaching the final density, thus having no manoeuvring ability if the obtained density is not correct, possibly producing sensitizing errors or an incorrect distribution of explosives in the column of the shot hole.
Another alternative is to transport the original product and sensitize it in the mine using the mixture of low density nitrate particles or a blend of ammonium nitrate with oil (ANFO). U.S. Pat. No. 4,555,278 and EP 0 194 775 describe explosives of this kind formed from emulsions and watergels respectively. In this type of explosive, known as “heavy ANFO”, the sensitization is due to the porosity of the granules of porous ammonium nitrate and the air occluded between the gaps thereof. These types of blends are not pumpable, the shot holes are loaded with spindles and its water resistance is limited. The nitrate particle content is generally higher than 50%, given the fact that for lower contents the density of the resulting blend is greatly increased once the liquid product fills the gaps, leading the mixture to loose initiation sensitivity. For nitrate particle contents of less than 50% the resulting product may generally be pumped and sensitization is carried out either before filling the shot holes with hollow microspheres or instead by generating gas once the shot holes have been filled through a chemical reaction.
The solution of patent WO 99/00342 (Unión Española de Explosivos S.A.) discloses a process and installation for the “in situ” sensitization of water-based explosives before loading the shot holes using a non-explosive watergel type matrix. Sensitization is carried out by blending dosed quantities of the matrix product with a gas and a stabilizer of the gas bubbles. Likewise, the patent application WO 01/04073 (Unión Española de Explosivos, S.A.) discloses the process for the “in situ” manufacturing of water based explosives before loading the shot holes from a watergel-type oxidant matrix with an oxygen balance greater than 14%, a combustible material, a gas and a gas bubble stabilizer.
The object of the invention is an “in situ” manufacturing procedure of water-based, pumpable blends of explosives, with an (i) non-explosive watergel-type matrix, (ii) an air bubble stabilizing agent and optionally (iii) an oxidant or blend of an oxidant and a combustible material in granular form and/or (iv) a liquid combustible material. The density of the final product can be regulated according to the conditions of the process. This process allows for the density to be controlled and, therefore, the quality of the explosive product, before filling the shot holes, thus avoiding sensitivity errors due to inadequate density. It also allows the energy of the resulting explosive product to be varied acting on the proportions of the explosive matrix and the oxidant or the blend of oxidant and combustible material in granular form.